Among typical applications for remote pilot-operated valves, such as for automatic temperature, pressure and time switches, and particularly as solenoid valves, are refrigeration systems where they are often utilized for evaporator temperature control, defrost pump down and heat reclaim systems, for example.
A solenoid valve is an electronically operated device used to control the flow of liquids or gases in a positive, fully-closed or fully open mode. When energized, the solenoid coil provides a strong magnetic force which pulls a steel plunger up into the plunger tube thus opening up the valve orifice in a normally closed valve, thereby permitting the flow of liquids or gases. Pilot-operated valves are among the most widely used solenoid valves.
For servicing and maintenance purposes it is desirable that the normally remotely controlled pilot-operated valves be capable of being opened and closed manually. This is generally accomplished via manual override assemblies or mechanisms built into the valve assemblies. Generally such assemblies, in main piston type valves, take the form of cylindrical plugs that are manually threaded up from under the main valve piston and forcing same off its seating at high force load. A typical prior art construction of this type is set forth in U.S. Pat. No. 3,236,494 to Frantz. Other prior art structures often use rotatable plunger and cam mechanisms of the type typically set forth in U.S. Pat. No. 4,501,299 to Klimowicz et al.; U.S. Pat. No. 4,643,393 to Kogusi et al.; U.S. Pat. No. 4,916,437 to Gazzaz; and U.S. Pat. No. 5,285,814 to Pettersson et al. In the structure set forth in U.S. Pat. No. 5,271,599 to Kolchinsky et al., a cam-actuated control rod extends from the top of the valve through the solenoid sleeve to accomplish the override function.
However, none of these prior art constructions incorporate the dual purpose of overriding both the operator (such as a solenoid) and the main piston of a piston-type pilot-operated valve.